Peter Schols

CARNOY: A new digital measurement tool for palynology

Quantitative data play an important role in palynological research. With the advent of digital imaging in light and electron microscopy, palynologists now have the opportunity to perform measurements faster and more precisely than ever before. Several image analysis software packages already exist for these tasks, but they are often expensive, difficult to use or not adapted to the specific needs of palynologists. After studying the daily workflow of a palynologist, we designed CARNOY, an image analysis application written from the ground up for use in palynology and morphology. CARNOY offers an easy-to-use interface and several features to make measuring easier and faster. The program can export measurements to almost every other software package for further analysis and is available for free on the Internet.

A Plastid Gene Phylogeny of the Yam Genus, Dioscorea: Roots, Fruits and Madagascar

Abstract Following recent phylogenetic studies of the families and genera of Dioscoreales, the identification of monophyletic infrageneric taxa in the pantropical genus Dioscorea is a priority. A phylogenetic analysis based on sequence data from the plastid genes rbcL and matK is presented, using 67 species of Dioscorea and covering all the main Old World and selected New World lineages. The analysis used 14 outgroup taxa, including Trichopus Gaertn., Tacca J.R. & G. Forster, Stenomeris Planch., Burmannia L. and Thismia Griff. The main findings are: a) that a clade of rhizomatous taxa is sister to the rest of Dioscorea; b) the main Old World groups (such as the right-twining D. sect. Enantiophyllum) are monophyletic and c) there are two distinct lineages among the endemic Malagasy taxa. The consequences of the results for infrageneric classification of Dioscorea is considered, in particular the possibility of greatly simplifying the classifications of Knuth and Burkill. The results are also used to present novel hypotheses of character evolution in selected underground storage organ, inflorescence, fruit and seed characters and to discuss the origins of diversity in Dioscorea.

Palynological characters and their phylogenetic signal in Rubiaceae

In the 1990s Rubiaceae became a hot spot for systematists, mainly due to the comprehensive treatment of the family by Robbrecht in 1988. Next to the exploration of macromolecular characters to infer the phylogeny, the palynology of Rubiaceae finally received the attention it deserves. This article aims to present a state-of-the-art analysis of the systematic palynology of the family. The range of varíation in pollen morphology is wide, and some of the pollen features are not known from other angiosperm taxa; e.g., a looplike or spiral pattern for the position of apertures in pantoaperturate grains. We compiled an online database at the generic level for the major pollen characters and orbicule presence in Rubiaceae. An overview of the variation is presented here and illustrated per character: dispersal unit, pollen size and shape, aperture number, position and type, sexine ornamentation, nexine pattern, and stratification of the sporoderm. The presence/absence and morphological variation of orbicules at the generic level is provided as well. The systematic usefulness of pollen morphology in Rubiaceae is discussed at the (sub)family, tribal, generic, and infraspecific levels, using up-to-date evolutionary hypotheses for the different lineages in the family. The problems and opportunities of coding pollen characters for cladistic analyses are also treated.

Pollen Evolution in Yams (Dioscorea: Dioscoreaceae)

Abstract Pollen character evolution in yams (Dioscorea: Dioscoreaceae) was investigated in relation to the phylogeny obtained from a recent combined analysis of rbcL and matK gene sequences. The following characters were evaluated: pollen size, aperture number, sexine ornamentation, perforation density, and orbicule presence or absence. Continuous characters were coded using the gap weighting method. Each character was optimized using MacClade onto a tree selected at random from analyses based on molecular data of Wilkin et al. The results indicate that in Dioscorea pollen size decreases in the more derived clades. The latter observation may be related to the evolution of annually replaced tubers. Aperture number increases from one in the monosulcate Stenophora clade (sister to the rest of Dioscorea) to two in other Dioscorea clades. This may be related to the presence of simultaneous microsporogenesis in Dioscorea. A perforate sexine is plesiomorphic in Dioscorea and a striate pattern has evolved more than once and is particularly characteristic in the Malagasy clade. Sexine ornamentation in the Stenophora clade is diverse. The endemic allotetraploid D. pyrenaica is characterized by large, monosulcate, gemmate pollen. The Dioscorea B clade is characterized by pollen with small, dense perforations. Orbicules occur in all Dioscorea species, but are absent in most of the outgroup taxa.

A new enzyme-based method for the treatment of fragile pollen grains collected from herbarium material

Although the majority of systematic palynologists use Erdtmans acetolysis method or the slightly modified method of Reitsma for the preparation of pollen grains for LM and SEM observations, these methods have some major drawbacks. Especially within monocots, pollen grains are often thin-walled, and therefore tend to collapse even after a mild acetolysis, as experienced, for instance, in Cyperaceae and Dioscoreaceae, among other groups. Very satisfying results often are obtained by the use of fresh material. Unfortunately, this is not available in most cases, especially when working on tropical taxa-hence making herbarium material indispensable. We present a comparison between three major methods for the treatment of fragile pollen (KOH/CPD-treatment, glutaraldehyde/CPD-treatment, and a mild acetolysis) and introduce a new enzyme-based method using cellulase and pectinase. All four methods are tested on three different monocotyledons of three different orders: Allium ursinum L. (Liliales), Asparagus officinalis L. (Asparagales), and Tamus communis L. (Dioscoreales). The properties and results of each method are then critically assessed. The new method yields satisfying results especially on the hydration state and shape of the pollen grains.

Comparative Pollen Development in Dioscoreales

Pollen and orbicule ontogeny in representatives of three genera of Dioscoreales—Narthecium ossifragum Huds. (Nartheciaceae), Tacca artocarpifolia Seem. and Tacca chantrieri André (Dioscoreaceae), and Dioscorea communis (L.) Caddick & Wilkin (Dioscoreaceae)—is described and illustrated using LM, SEM, and TEM. The main difference is in microsporogenesis, which is successive in Narthecium Huds. and simultaneous in Tacca J.R. & G. Forst. and Dioscorea L. This is reflected in the tetrad configuration but not in the apertures: Narthecium and Tacca are monosulcate, while Dioscorea has two equatorial apertures. Other features of pollen development are similar in all three genera. Exine development starts at the proximal pole, and during the tetrad stage, the exine remains thicker at this pole. Intine development begins before mitosis. A conspicuously channeled intine forms beneath the aperture(s) in all three genera, and in Tacca it also occurs in nonapertural regions. After mitosis, the generative cell is situated at the proximal pole in all genera. Orbicules are present in Narthecium and Dioscorea but not in Tacca, although it has a secretory tapetum. In the tetrad stage, pro‐orbicules appear on the tapetum in Narthecium and Dioscorea, and pro‐sporopollenin is consequently deposited to form the orbicule wall.

A new species of Dioscorea (Dioscoreaceae) from Western Madagascar and its pollen morphology

A new species of Dioscorea, D. namorckensis, from the Reserve Naturelle Integrale de Tsingy de Namoroka in Western Madagascar is described and illustrated, and its macromorphology and pollen morphology are presented. It is closely related to D. soso Jum. & H. Perr., and belongs in Dioscorea sect. Brachyandra Uline. It is found in the understorey and margins of deciduous forest on karst limestone, and appears to be endemic to Namoroka.

Dioscorea ridleyi and D. palawana: new systematic data on two rare South-East Asian yam species

Dioscorea ridleyi Prain & Burkill and D. palawana Prain & Burkill were previously described from limited material of one sex. Recent collections of plants of the other sex have come to light in both species. These are used to complete morphological descriptions of the two species. Both species appear to be of very restricted distribution. The new data allows reappraisal of the relationships of the two species to each other and with D. sect. Stenophora Uline, in which they were placed by Prain & Burkill. Their unique cerebroid perforate pollen ectexine morphology and several macromorphological characters suggest either that they do not belong in D. sect. Stenophora or that they are a highly specialised group nested within it.